Published in IET Generation, Transmission & Distribution Received on 9th October 2008 Revised on 23rd January 2009 doi: 10.1049/iet-gtd.2008.0520 ISSN 1751-8687 FPAA-based mho distance relay considering CVT transient supervision M.R. Dadash Zadeh 1 T.S. Sidhu 1 A. Klimek 2 1 Department of Electrical & Computer Engineering, University of Western Ontario, London, Canada 2 Areva T & D E-mail: mdadashz@uwo.ca Abstract: Present-day numerical relays provide remarkable capabilities such as monitoring, recording and communication. These capabilities are considered as secondary priority whereas speed and reliability are the two most important characteristics of a protective relay. Even though present-day numerical relays have provided considerable capabilities and advantages, they have not improved speed of operation in comparison to their solid-state counterparts. The idea of applying mixed signals processing using advanced analogue and digital technology in several applications has started. Use of advanced programmable analogue technology, which is known as field programmable analogue arrays (FPAAs), seems to have the potential to be used in protective relays. Hybrid hardware using both digital signal processor (DSP) and FPAAs is proposed to implement mho distance relay considering capacitor voltage transformer (CVT) transient supervision for low and high system impedance ratio (SIR) systems. Test results are reported and compared with a commercial relay test results. 1 Introduction Solid-state relays introduced in industry during 1960–1990 are relatively fast with operating times close to half a cycle for some distance relays since they were dealing with instantaneous voltage and current signals. They are based on the use of analogue electronic devices such as transistors, operational amplifiers, transistors, diodes in conjunction with resistors, capacitors, inductors etc. [1, 2]. This makes their hardware very complicated and less flexible whereas the protection principle used was proven to be simple, appropriate and faster. Digital relays use microprocessor and analogue-to-digital (A/D) converters to perform protection functions [2, 3]. In order to mimic the same technique used in solid-state relays in microprocessor-based relays to achieve the same performance, infinite impulse response (IIR) filters must be implemented in numerical algorithms. Microprocessor relays are unable to implement accurate IIR filters because of quantisation errors and error accumulation. This prevents the use of the same instantaneous-signal-based methods as used in solid-state relays [4, 5]. Because of this reason, phasor-based algorithms using finite impulse response (FIR) filters have been applied in most of the numerical relays resulting in higher operating times close to one cycle compared to their solid-state equivalent relay. Present-day numerical relays are very flexible. They are adjusted through keypad or personal computer link. Implementation of an analogue relay using conventional analogue technology with similar capabilities and flexibilities of present-day numerical relays is very complicated. Field programmable analogue array (FPAA) is a switch- capacitor-based integrated circuit in which a variety of analogue circuits can be implemented quickly and easily. FPAA features: † higher accuracy compared to the conventional analogue technology, † programmability on the fly and † no quantisation is involved in this technology. The last feature enables implementation of IIR filters in FPAAs. These features provide enough potential to use 616 IET Gener. Transm. Distrib., 2009, Vol. 3, Iss. 7, pp. 616–627 & The Institution of Engineering and Technology 2009 doi: 10.1049/iet-gtd.2008.0520 www.ietdl.org